The present disclosure generally relates to a transfer switch that is interconnected with both a utility power source and an auxiliary power source, such as an electrical generator, for controlling the supply of electric power from either the utility or the generator to electrical circuits in a home or business. More specifically, the present disclosure relates to a transfer switch that allows connection and disconnection of the neutral for the utility or generator for a whole house using the transfer switch.
Generators are used in a variety of different environments. For example, a generator can be used as an auxiliary or back-up power source for a building (e.g., a residence) or as the primary power source at a construction site. Numerous other uses for a generator are possible.
Bonding the neutral wire or line of the generator to ground is required in some environments. For example, the U.S. Occupational Safety & Health Administration (“OSHA”) and the U.S. National Electrical Code (“NEC”) require some generators to be neutral bonded, i.e., electrically connecting the neutral line of the generator to ground. Also, it may be required to include a ground-fault-circuit interrupt (“GFCI”) in some generators for detecting ground-fault current.
A circuit breaker panel of a building or residence also typically has the neutral line bonded to ground. If a generator is connected to such a circuit breaker panel, a loop is created with the neutral line of the generator and the ground line of the circuit breaker panel. This potentially induces a current through the neutral and/or ground lines, or creates multiple paths to ground, which trips the GFCI of the generator or in the building.
Presently, many local jurisdictions require the neutral of a back-up generator to be switched, and thus completely isolated from the utility, during transfer of power supply from the utility to the generator during a loss of power. The requirement that neutral be switched falls in line with the requirement that line voltages must also be isolated during transfer between the utility and the generator. Presently, three-phase transfer switches are used to isolate the neutral in jurisdictions having this requirement. However, the cost of a three-phase switch can be an impediment to installing a back-up generator.